EFFECT OF THERMOMECHANICAL PROCESSING ON THE PRECIPITATION BEHAVIOUR OF A COBALT-BASED SUPERALLOY

Abstract

Superalloy development is prompted by the need of high strength at high temperature and requirement, of heat resistant materials in aircraft -engine turbo superchargers, and gas turbine engine. The super alloys in use are either cobalt-base, nickel-base or iron-base. The alloy under investigation is super Co-605 has nominal composition: Cr-10.%, Ni-15%, W-3%, Fe-1.5%, Mn-0.08% and C-0.3% (maximum) and Co-balance. Cobalt-base alloys have additional advantages in hot corrosion type applications due to high chromium content, and its very flat stress rupture, makes them of a particular " value for long-lived static parts which often serve at lower stress but at high temperatures. Co-base alloys also exhibits a superior thermal fatigue resistance and weldability which makes them an unavoidable materials in gas turbine'engine. The alloy under investigation is homogenized at 1250°C for 1.50hrs followed by water quenching, which yields a completely homogenized structure with a hardness value of 106.47VHN. On ageing the various carbides viz. M23C6, M6C and MC got precipitated along grain boundary and within grains. Thermomechanical ageing treatment affects the size, shape and distribution of these precipitated particles and enhances the peak value by- 50% and reduces the time for achieving this enhancement.